US President Joe Biden marked the 80th anniversary of D-Day on Thursday by saying “we will not walk away” from the defence of Ukraine and allow Russia to threaten more of Europe.

“To surrender to bullies, to bow down to dictators, is simply unthinkable,” he said during a ceremony at the American cemetery in Normandy. “If we were to do that, it means we’d be forgetting what happened here on these hallowed beaches.” D-Day was the largest amphibious assault in history, and Biden called it a “powerful illustration of how alliances, real alliances make us stronger”. He said that was “a lesson that I pray we Americans never forget”.

The comment by the Democratic President was a reminder that US commitments around the globe hang in the balance in this year’s White House election. Donald Trump, the presumptive Republican nominee, has said he would not defend European allies that are “delinquent” in their own security spending.

The former President also has expressed little enthusiasm for Ukraine’s defence, criticising the “endless flow of American treasure” and voicing admiration for Russian President Vladimir Putin.

Biden, who is expected to meet Ukrainian President Volodymyr Zelensky in Paris on Friday, hopes new deliveries of US munitions after months of delay can help stem Russian advances on the battlefield.

In his remarks, Biden cited the American troops that stormed Normandy’s beaches on June 6, 1944, and said “Let us be worthy of their sacrifice”.

“We must remember that the fact that they were heroes here that day does not absolve us of what we have to do today,” he said. “Democracy is never guaranteed. Every generation must preserve it, defend it and fight for it. That’s the test of the ages.”

Before Biden’s remarks, French President Emmanuel Macron told US veterans: “You came here because the free world needed each and every one of you, and you answered the call.” Macron awarded the Legion of Honour to several of them, and he kissed them on each cheek as he pinned on their medals. Biden followed with handshakes and embraces.

Earlier, Biden and First Lady Jill Biden met more than two dozen American veterans near Omaha Beach, where the fiercest D-Day fighting took place. Those who could stand were helped out of wheelchairs to pose for photos. Most shook hands with Biden or saluted; one hugged him. Biden told a veteran: “You saved the world.” The President led the audience in singing Happy Birthday to another.